In thermal recovery processes for heavy oil production employing steam flooding, channeling and override problems are common. Channeling is due to the high mobility ratio of the displacing fluid (steam) and the low mobility of the displaced fluid (heavy oil). It can also be caused by high permeability zones (theif zones) which could exist in the reservoir. The override effect occurs because of the density difference between the steam and the oil. When either of these phenomena occurs, steam tends to break through early at the production wells and bypass a considerable volume of the reservoir.
Currently there is no proven technology to prevent steam channeling and override. Efforts have been concentrated on developing a good surfactant chemical for coinjection with steam. The surfactant is intended to foam in-situ, thus reducing steam mobility and blocking thief zones. These surfactant chemicals, however, are costly and subjected to degradation due to high temperatures and reservoir pH changes (Al-Khafaji et al, SPE Paper No. 10777, presented at 1982 SPE California Regional Meeting, San Francisco, Mar. 24-26, 1982).